1. Field of the Invention
The present invention relates to a deodorized, polyether-modified polysiloxane composition, method for producing the same and cosmetic containing the same, more particularly a deodorized, polyether-modified polysiloxane composition not producing a substance giving off a foul odor, while being produced or stored, which results from hydrolysis, oxidation or the like of a by-product or unreacted material and temporarily stable, and method for producing the same and cosmetic containing the same.
2. Description of the Prior Art
A polyether-modified polysiloxane is traditionally synthesized by hydrosilylation in which a polysiloxane having hydrosilyl group is reacted with a polyoxyalkylene having an unsaturated bond.
The polyether-modified polysiloxane, however, involves a disadvantage of giving off a foul odor with the lapse of time, making itself difficult to be used for cosmetics, e.g., those for the hair or skin.
This disadvantage was considered to result from deterioration of the polyether-modified polysiloxane by oxidation which occurs with the lapse of time to form aldehyde. However, another cause is reported. For example, JP-A-2-302438 discusses that a foul odor results from an unreacted, propenyl-etherified polyoxyalkylene (refer to the claims or the like). More specifically, part of an allyl-etherified polyoxyalkylene is transformed into a propenyl-etherified polyoxyalkylene because of its double bond migrating inwards in the presence of a platinum catalyst while the polysiloxane composition modified with a polyether is being produced. As a result, it remains unreacted with an organohydrogen polysiloxane to be left in the polysiloxane composition modified with a polyether, and is decomposed with the lapse of time into a ketone or aldehyde to give off a foul odor. The patent document also discloses that the composition can be effectively deodorized by hydrolysis in the presence of an acid. This deodorizing approach will be effective for removal of the unsaturated group, when the allyl group in the residual polyoxyalkylene is totally transformed into propenyl group. In actuality, however, the allyl-etherified polyoxyalkylene undergoing no rearrangement remains to some extent to reduce the deodorizing effect, because the isomerization in the presence of a platinum catalyst reaches an equilibrium. In other words, the approach disclosed by the above patent document involves a problem of insufficient acid strength for hydrolysis of an allyl-etherified polyoxyalkylene.
Hydrolysis of an allyl-etherified polyoxyalkylene in the presence of a stronger acid is not adequate, because of the possible scission of the carbon-oxygen bond in the polyoxyalkylene or silicon-oxygen bond in the polysiloxane.
Moreover, the hydrolysis needs excessive quantities of water and acid in order to proceed quantitatively, which introduce greater complexity into the post-treatment. Therefore, the above deodorization approach is not ideal. Still more, the foul odor results not only from the carbon-carbon double bond but also from unstable oxides or the like difficult to identify. This is another problem involved in the above approach.
In consideration of the disadvantages involved in the deodorization based on the hydrolysis in the presence of an acid, varied solutions have been proposed to control formation of odorous substances by hydrolysis, oxidation or the like of polyether-modified polysiloxane. For example, U.S. Pat. No. 5,225,509 discloses a method for deodorizing a polyoxyalkylene polysiloxane by hydrogenation under the conditions of temperature: 20 to 200° C., pressure: 1 to 100 bars and reaction time: 0.5 to 10 hours in the presence of a hydrogenation catalyst (refer to the claims or the like). JP-A-7-330907, 9-165315 and 9-165318 disclose that a polyether-modified polysiloxane composition, synthesized by hydrosilylation in which a polyoxyalkylene having the carbon-carbon double bond at the terminal is reacted with an organohydrogen polysiloxane, can be temporarily stable without giving off a foul odor, when hydrogenated (refer to the claims or the like).
However, the composition treated only by hydrogenation may still contain an aldehyde condensate, e.g., acetal, which can be transformed into the aldehyde in an aqueous solution to cause foul odor. This is because hydrogenation alone cannot sufficiently treat an aldehyde condensate, which lacks an unsaturated bond, to remove odorous substances.
In consideration of the above problems, WO-02/055588, for example, proposes a deodorized, modified silicone compound having a degree of unsaturation and aldehyde formed each controlled at a specific level or less, and cosmetic containing the same, where the modified silicone compound is refined by (A) hydrogenation of the residual unsaturated bond and subsequent decomposition of an aldehyde condensate in an acid-containing, aqueous solution kept at a pH of 7 or less, or (B) decomposition of a propenyl-etherified product in an acid-containing, aqueous solution kept at a pH of 7 or less and subsequent hydrogenation of the aldehyde formed and residual unsaturated bond (refer to claims or the like).
The above proposal, however, needs treatment in an acid-containing, aqueous solution kept at a pH of 7 or less as the essential step. Therefore, the acidic substance in the aqueous solution is dissolved and hence remains in the system. As a result, the acid treatment should be generally followed by a neutralization step, and the salt formed by the neutralization also partly remains in the system. Thus, the above proposal involves the problems that the acid substance and salt by the neutralization remain in the system. In particular, a polyether-modified polysiloxane is more hydrophilic than a dimethyl polysiloxane, and allows the acidic substance and salt by neutralization to remain in the system to a higher content. These residual substances cause another problem of retarding the hydrogenation step, when it follows the neutralization step.
Moreover, a polyether-modified polysiloxane containing trace quantities of the acidic substance and salt by neutralization also involves a problem of causing a foul smell of the system with the lapse of time, when it comprises water and a polyhydric alcohol, conceivably resulting from, e.g., the residual substances themselves or a decomposition product thereof, or a decomposition product of the polyether-modified polysiloxane.